I think you're all missing the point, half of these places were known for hamburgers, the other half for whole pieces of fried chicken. They all ended up with slight variations on the same product. The point isn't that they should've innovated the chicken sandwich it's that they all ended up with the same product, the opposite of innovation in a market full of restaurants.
In the real world, people often eat in groups. Some overlap is to be expected, especially when what is really being sold isn't a chicken sandwich, it's addictive convenient food.